1. Field of the Invention
Example embodiments generally relate to a separator, a separation device, a fixing device, and an image forming apparatus, and more particularly, to a separator for separating a recording medium from an endless belt, a separation device incorporating the separator, a fixing device for fixing a toner image on a recording medium and incorporating the separation device, and an image forming apparatus incorporating the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device is requested to shorten a first print time required to output the recording medium bearing the toner image onto the outside of the image forming apparatus after the image forming apparatus receives a print job. Additionally, the fixing device is requested to generate an increased amount of heat before a plurality of recording media is conveyed through the fixing device continuously at an increased speed.
To address these requests, the fixing device may employ a thin endless belt having a decreased thermal capacity and therefore heated quickly by a heater. FIG. 1 illustrates a fixing device 20R1 incorporating an endless belt 100 heated by a heater 300. As shown in FIG. 1, a pressing roller 400 is pressed against a tubular metal thermal conductor 200 disposed inside a loop formed by the endless belt 100 to form a fixing nip N between the pressing roller 400 and the endless belt 100. The heater 300 disposed inside the metal thermal conductor 200 heats the entire endless belt 100 via the metal thermal conductor 200. As the pressing roller 400 rotating clockwise and the endless belt 100 rotating counterclockwise in FIG. 1 convey a recording medium P bearing a toner image T through the fixing nip N in a recording medium conveyance direction A1, the endless belt 100 and the pressing roller 400 apply heat and pressure to the recording medium P, thus fixing the toner image T on the recording medium P.
Since the metal thermal conductor 200 heats the endless belt 100 entirely, the endless belt 100 is heated to a given fixing temperature quickly, thus meeting the above-described requests of shortening the first print time and generating the increased amount of heat for high speed printing. However, in order to shorten the first print time further and save more energy, the fixing device is requested to heat the endless belt more efficiently. To address this request, a configuration to heat the endless belt directly, not via the metal thermal conductor, is proposed as shown in FIG. 2.
FIG. 2 illustrates a fixing device 20R2 in which the heater 300 heats the endless belt 100 directly. Instead of the metal thermal conductor 200 depicted in FIG. 1, a nip formation plate 500 is disposed inside the loop formed by the endless belt 100 and presses against the pressing roller 400 via the endless belt 100 to form the fixing nip N between the endless belt 100 and the pressing roller 400. Since the nip formation plate 500 does not encircle the heater 300 unlike the metal thermal conductor 200 depicted in FIG. 1, the heater 300 heats the endless belt 100 directly, thus improving heating efficiency for heating the endless belt 100 and thereby shortening the first print time further and saving more energy.
On the other hand, the fixing devices 20R1 and 20R2 may include a separator situated downstream from the fixing nip N in the recording medium conveyance direction A1 to contact and separate the recording medium P discharged from the fixing nip N from the endless belt 100. For example, the separator includes legs that pressingly contact both lateral ends on the outer circumferential surface of the endless belt in the axial direction thereof to remove slack from the endless belt and at the same time position the separator with respect to the outer circumferential surface of the endless belt.
If the separator is installed in the fixing device 20R1 shown in FIG. 1, the rigid, tubular metal thermal conductor 200 supporting the endless belt 100 throughout the entire width in the axial direction thereof prevents the flexible endless belt 100 from being deformed by pressure from the legs of the separator. Conversely, if the separator is installed in the fixing device 20R2 shown in FIG. 2, the nip formation plate 500 supporting the endless belt 100 only at the fixing nip N cannot support the endless belt 100 against pressure from the separator at the position downstream from the fixing nip N in the recording medium conveyance direction A1. Accordingly, the endless belt 100 may be deformed by pressure from the separator. Consequently, the separator with the legs contacting the deformed endless belt 100 may be positioned with respect to the outer circumferential surface of the endless belt 100 improperly. For example, an uneven interval may be produced between the separator and the outer circumferential surface of the endless belt 100 throughout the entire width in the axial direction thereof, resulting in faulty separation of the recording medium P from the endless belt 100. Further, the separator may strike the endless belt 100, resulting in abrasion or breakage of the endless belt 100.